The present invention relates to the field of medical imaging. It concerns a collimator intended to be mounted in a detector of a medical imaging system and, in particular, in a gamma camera detector.
Gamma cameras are medical imaging systems provided with at least one detector intended to pick up gamma radiation emitted by a patient, into whose body a gamma-emitting radioisotope marker has been injected. This gamma radiation passes through a collimator and excites a scintillator crystal which converts the energy of said gamma radiation into light energy that is detected by photomultiplier tubes which then produce electrical signals as a function of the luminous intensity received. By performing center-of-gravity location over all these electrical signals, it is possible in known fashion to determine the origin of each scintillation. Taken together, these scintillations make it possible to acquire, for a given angle of view of the detector, a projection revealing the concentration of the gamma-emitting radioisotope marker in the patient's body and, with several projections, obtained for different angles of view, an image of a cross section or a volume of the patient's body is reconstructed.
The collimators are placed in front of and against the detectors, at the entry face of the scintillator. They consist of an absorbent plate pierced by holes whose characteristics, in particular cross section, height, inclination and vergence, are identical. The field of view of the collimator is unique and unitary. Thus, the holes select the gamma rays emitted or transmitted by the patient's body in a given solid angle whose axis is parallel to the direction of the projection which is acquired, whereas the gamma rays that do not correspond to this solid angle are absorbed by partitions delimiting the holes in the collimator.
Certain examinations require the presence of a collimator having very high resolving power, that is to say in which the aforementioned solid angle is narrow, whereas other examinations do not require collimators of this type. For this reason, the collimators of a gamma camera are changed in accordance with the examinations that are performed. Various more or less complex methods have moreover been proposed to this end. One of these methods is described in the French patent published under number FR-2,640,054 and entitled: "systeme de mise en place d'un collimateur dans une gamma camera" system for fitting a collimator in a gamma camera!.
In view of the above considerations, the invention proposes to solve the problem of producing a collimator which can be used in different examinations, without needing to be changed.